Many vehicles utilize exhaust gas recirculation (EGR) to meet increasingly stringent emissions standards. By using EGR, an in-cylinder temperature may decrease, thereby reducing the formation of NOx and other pollutants. However, EGR is not treated and/or filtered before being diverted from the exhaust passage to an intake manifold. Thus, the EGR may still comprise liquid fuel and/or combustion by-products, which may degrade an EGR valve.
Such malfunctioning may be caused by a portion of the EGR valve being unable to open from its closed position due to accumulated deposits of combustion products on the valve. This type of malfunctioning normally occurs during a cold-start. If a control system used to control opening and closing of the EGR valve tries to open the EGR valve after the engine has been started from cold and the valve is stuck then it will not open or will open slowly and in either case an error code indicating the malfunction of the EGR valve will be generated.
The deposits are generally exhaust products, primarily soot and hydrocarbon, which condense and coalesce on a stem of the valve during engine cooling and then harden as they cool. When the valve is hot, these deposits are soft and the valve can be opened and closed normally. However, by the time that the valve has been heated sufficiently after an engine start to soften the deposits, an EGR valve malfunction will already have occurred, been detected and been indicated.
Attempts to address exhaust gas recirculation valve degradation include actuating the valve following an engine shut-off event. One example approach is shown by Enomoto in U.S. Pat. No. 7,832,373. Therein, the cleaning cycle typically involves sweeping the valve over its full range of movement a number of times.
However, the inventors herein have recognized potential issues with such systems. As one example, by cleaning the EGR valve directly after an engine shut-off, the dislodged particulates may still impinge onto surfaces of the valve due to a temperature of the valve being substantially similar to an operating temperature.
In one example, the issues described above may be addressed by an exhaust gas recirculation system for an engine of a motor vehicle comprising an exhaust gas recirculation passage connecting an exhaust gas outlet from the engine to an air inlet of the engine, an exhaust gas recirculation valve for controlling a flow of exhaust gas through the exhaust gas recirculation passage, and an electronic controller to control opening and closing of a valve of the exhaust gas recirculation valve during engine operation and to control the exhaust gas recirculation valve to perform at least one valve cleaning operation to remove deposits from the valve when the engine is deactivated, wherein the electronic controller is further operable to delay execution of the at least one valve cleaning operation following a shutdown of the engine to allow cooling of the valve to take place thereby reducing a likelihood that deposits will reform on the valve after the valve cleaning operation has taken place. In this way, an optimal cleaning temperature of the exhaust gas recirculation valve may be reached prior to performing the valve cleaning operation.
As one example, the electronic controller may be operable to enter a sleep mode during the delay between the shutdown of the engine and the start of the cleaning operation in order to reduce the consumption of electricity by the electronic controller. The electronic controller may have a timer to define the delay between the shutdown of the engine and the start of the cleaning operation. The length of the delay may be based upon a comparison of an output from the timer with a predefined time limit. The exhaust gas recirculation system may further comprise a temperature sensor arranged to provide a measurement of temperature to the electronic controller indicative of a temperature of the exhaust gas recirculation valve and the length of the delay between the shutdown of the engine and the start of the cleaning operation may be based upon a comparison of the measured temperature with a predefined temperature limit. The electronic controller may include a model of predicted relationship between temperature and time for the exhaust gas recirculation valve and the length of the delay between the shutdown of the engine and the start of the cleaning operation may be based upon a comparison of the predicted temperature with a predefined temperature limit. There may be two or more cleaning operations and the electronic controller may be operable to enter a sleep mode during a first delay between the shutdown of the engine and commencement of a first one of the cleaning operations and may be further operable to enter the sleep mode during respective delay periods between subsequent cleaning operations.
According to a second aspect of the present disclosure, there is provided a motor vehicle having an engine, at least one battery, a human machine interface to selectively start and shutdown the engine and an exhaust gas recirculation system constructed in accordance with said first aspect of the invention. The cleaning of the exhaust gas recirculation valve may only be permitted if a state of charge of the battery is above a predefined state of charge limit.
According to a third aspect of the present disclosure there is provided a method of cleaning an exhaust gas recirculation valve having a moveable valve, the method comprising delaying cleaning of the exhaust gas recirculation valve after shutdown of the engine to allow cooling of the valve to take place thereby reducing the likelihood that deposits will reform on the valve after the cleaning operation has been completed. The method may further comprise putting an electronic controller used to control operation of the exhaust gas recirculation valve into a sleep mode during the delay between the shutdown of the engine and the start of the cleaning operation in order to reduce the consumption of electricity by the electronic controller. The method may further comprise using a comparison of an output from a timer with a predefined time limit to determine the length of the delay. The length of the delay may be based upon a comparison of a measured temperature of the exhaust gas recirculation valve with a predefined temperature limit. The length of the delay may be based upon a comparison of a predicted temperature of the exhaust gas recirculation valve with a predefined temperature limit. The method may comprise using two or more cleaning operations to clean the exhaust gas recirculation valve and an electronic controller used to control the exhaust gas recirculation valve may be put in a sleep mode during the delay between the shutdown of the engine and the start of a first one of the cleaning operations and the electronic controller may also be put into the sleep mode during respective delay periods between subsequent cleaning operations.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.